1. Field of the Invention
The present invention relates to a magnetic position sensor, and in particular to a position sensor for generating a signal corresponding to the position of a magnetic test object moveable along and out of contact with a core of low magnetic retentivity between two excitation coils which magnetize the core.
2. Description of the Prior Art
A magnetic position sensor is described in the periodical Technisches Messen, Vol. 50, No. 10, 1973 at pages 373-378, which has an elongated rectangular magnetic core with a primary winding and a secondary winding respectively disposed at the opposite shorter sides of the rectangle. A test object whose position is to be identified by the position sensor is in the form of a short-circuit ring which surrounds one of the longer sides of the low-coercivity core. The short-cirucit ring generates a virtual air gap (i.e., simulates an air gap) in the low-coercivity core at a location corresponding to the position of the ring between the primary and secondary windings. An air gap is simulated because the short circuit currents induced in the core at the location of the test object substantially prevent the magnetic core from carrying a magnetic flux at that location.
If the test object (short-circuit ring) is situated in the middle of the elongated leg of the low-coercivity core, the two magnetic systems, respectively consisting of the primary and secondary coils, have the same stray field, so that the voltages generated in pick-up coils will be equal to each other and will cancel each other in a differentiating circuit.
When the test object is moved away from the middle position laterally along the longer side of the rectangle, the induced voltage in one of the pick-up windings is increased and the other is diminished. A voltage having a magnitude dependent upon the position of the test object is thus obtained, so that the path traversed by the test object can be identified.